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How loud was the Concorde's sonic boom at the ground level?
Before the Concorde was sent into retirement, their supersonic flight paths were restricted to the ocean because of concerns about sonic boom on the ground.
But just how loud was this boom? Was it significantly louder than the noise from a Mach 0.9 airplane?

The sonic boom of the Space Shuttle generated a pressure of 60 Pa on the ground, from an altitude of 18 km, the Concorde 93 Pa -- that is 133 dB -- from an altitude of 16 km. See this article on sonic boom.

Concorde was louder than a 0.9 aircraft when it was subsonic!.  The sonic boom is at 0:58 in the same video.

@Simon yes but that's take off. I'm wondering how loud it was in-flight.

Keep watching.  As I said, the boom is at 0:58.

@JonathanReez: Concorde sonic boom was very much louder (at the same altitude) than flying at M 0.9. 133 dB is above pain threshold for most people (discomfort is between 85 and 95 dB SPL and the threshold for pain is between 120 and 140 dB SPL). After pain threshold, no one can say if "this is louder" as ear is saturated. See this comparison.

@mins but didn't the boom last for a split second for an observer on the ground? Basically I'm trying to understand just how bad it would be if supersonic jets were flying around all the time.

You last comment is a too broad to be answered here (would jets flying around all the time be a pain, so taking into account duration of exposure and mean level), there is a lot of literature online on the topic. Have a look at the last link I posted ("Military jet aircraft take-off from aircraft carrier with afterburner at 50 ft = 130 dB"). 10 dB SPL difference is factor 2 in the ear sensation (sound twice louder).

@mins please don't answer questions in a comment

Anecdotally: I remember visiting Hampton Court Palace as a child  on a school trip, which was right below concorde's flight path (into heathrow I suspect). The tour guide had to stop her blurb for a good 90 seconds whilst it flew overhead. That was so far from supersonic, but it was still the loudest thing short of a Vulcan bomber I remember aviation-wise.

Forgive my ignorance, I'm new, but why was this question marked as duplicate. The other question answers whether a sonic boom at 60K' can be heard on the ground. I read that other answer and it doesn't directly answer  Mr @JonathanReez question of whether the Concorde's sonic boom was "significantly louder than the noise from a Mach 0.9 airplane", as is asked in this question.

@Devil07 I marked it because it directly answered my question.


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Is A380's center of gravity really too far back?
I have searched and even studied plans from Airbus itself, but I was not able to confirm the following and would like to ask if the information I have is correct.
TLDR version so you don't have to read all the text: Does A380 really have the center of gravity positioned BEHIND the aerodynamic force center?
(What I know so far): For any passenger aircraft, without (almost any) exception, the center of gravity is always closer to the nose of the aircraft than the aerodynamic forces resultant. This is to provide an auto-stabilising force for the aircraft in case it stalls for whatever reason. Since the airplane is "nose heavy", it would eventually establish itself "towards the air flow" and after some height drop, should at least partially regain normal flight mode. Also it prevents the aircraft from going into a flat loop. While this setup is safe, it also means that the tail wing needs to correct for the center of gravity and "pull down" (omitting the duck planes now), which means it does not help to create lift, instead reducing the total lift. This increases fuel consumption.
(What I need to confirm): During my UL theory training, one of the instructors told us that A380 (and all the new passenger planes driven mostly by computers alike) will have the center of gravity behind the aerodynamic center, which enables to use the huge tail wing to actually create lift instead of decreasing it and thus lowering the fuel consumption dramatically. While this is great from economical and ecological point of view, it would only work while the computers look after the plane. It would become so unstable that there is no way a human could fly it "by hand".
I understand that if the computers go down on a "fly-by-wire" airplane completely, the joystick/rudder becomes just a piece of plastic anyways, but a computer that constantly looks after the stability of the plane seems much more "error ready" than a simple wire between a cockpit and a servo.
Modern jet fighters have CoG behind the aerodynamic center and it is said that you only stall them once. There is no way to recover a stall like you would do with your good old Cessna. It strikes me that something like that would get approved for a civilian aircraft.
Thank you for your inputs. I was not able to find any resource concerning A380's CoG.

The idea that no human could control an inherently unstable aircraft is a myth. While some fighter aircraft are designed to be extremely unstable, making human reaction times too slow, I would not expect an aircraft with such a large mass moment of inertia to be unstable under human feedback.

@Sanchises: Just my personal opinion, but I would expect it to behave exactly the opposite way. Given the mass and length of the aircraft, even a slight shift in the center of gravity would necessarily create a huge leverage arm, which would quickly turn a "not stable aircraft" into a falling brick. Is my idea wrong? If the CoG is behind the aerodynamical center and the leverage is long and strong, then the pilot should have zero chance of turning the nose back to the right direction.

@user27978 What matters is not how heavy the plane is but how unstable it is. The argument in your comment is very similar to "A heavy object must fall extremely quickly because of the huge gravitational force acting on it." Well, no, because the huge force also has to accelerate a huge mass. Mass cancels out.

Moments scale linearly with size, mass moments of inertia quadratic, so rotation is slower. Mass cancels out. Of course, mass is cubic to size, area quadratic, so one needs disproportionally large control surfaces (note the massive tail fin on an A380). So, a large aircraft will not depart as quickly from forward flight (large phase margin), but will require harder control actions to get it back in line (gain margin).

Of course, none of the above actually answers the question, but unstable systems are not the worst thing that can happen in engineering, by far. Compare with the B52's anhedral to reduce roll stability - too much stability equals very slow maneuverability.

Related: Will optimising the weight distribution of a commercial flight save fuel?

No time right now for an exhaustive answer, but the fact alone that net force from both wing and stabiliser are upwards does not automatically make the aircraft unstable.

Funny - this is the first time I encountered the expression "duck aircraft". Maybe English should follow German and translate that French word also.

@Sanchises: "The idea that no human could control an inherently unstable aircraft is a myth."  Indeed, the 1903 Wright Flyer was one such aircraft.

No. Positive lift on the tail does not necessarily mean that the center of gravity needs to be aft of the aerodynamic center of the aircraft. Only when the lift per area of the tail surface is higher than that of the wing will the center of gravity move into the unstable region.

the center of gravity is always closer to the nose of the aircraft
  than the aerodynamic forces resultant

Again, no. The center of gravity needs to be at the same lengthwise station as the center of pressure in trimmed flight, otherwise the aircraft would not be trimmed and start to pitch. With low-mounted engines there might be some thrust moment which must be canceled by a slightly forward location of the center of gravity, but this effect is small.
Next, the auto-stabilisation is not only helpful when stalling. It also provides a smoother ride in gusty conditions and makes it easier for the pilot to fly the aircraft.
Since the aspect ratio of the tail surfaces is smaller than that of the wings, lift there is bought more expensively, so it will be bad for performance if the tail produces more lift per area than the wing. Negative stability is only helpful for supersonic and highly manoeuverable airplanes. Airbus does not do that, and besides, the A380 would not be certified with negative stability.
What it does have, however, like all Airbus aircraft since the A310, is relaxed static stability. The center of gravity is still ahead of the neutral point, but less so than in conventional airliners. This does indeed help to lower drag, and the reduced (but still positive!) stability is enhanced by electronic means.

If the CoG is still ahead of the neutral point is the horizontal stabilizer on an A380 indeed producing positive lift during level flight?

Yes. Less per area than the wing, but still positive. Only when you move it further forward there is a point when lift on the tail is zero. Then the center of gravity is where the center of pressure of the wing-fuselage combination is. Now move it even more forward, and lift on the tail turns negative.

Wouldn't any lift of the horizontal stabilizer other than zero cause the aircraft to pitch about the CG?  (regardless of the location of the CG)

@MichaelHall: There are pitching moments from the wing which need to be balanced by lift (positive or negative) at the tail. Only when all wing lift acts at the lengthwise station of the cg will zero lift at the tail be needed for steady flight.

I asked the question to an A380 pilot today and he confirmed that the stabiliser has positive lift, and that therefore the CG is behind the centre of lift of the main wings. According to him the A380 Has fuel trim that transfers fuel from tail to main tanks. He used to fly A330 and stated that direct law in A380 is easier and more stable than in the A330.

If A380 is more stable in direct law—and in fact since it is flyable in direct law at all—it must be positively stable. That makes the answer a clear and resounding NO.

Note that the tail might be providing positive lift, at least with CoG at the aft limit and high speed. But that does not yet make the plane unstable—the lift would have to fly at higher coefficient of lift than the main wing for that. It does not. That is only done on fighters.

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Has the Boeing 737 MAX MCAS system successfully prevented a stall or approach to stall condition outside testing?
The Boeing 737 MAX MCAS system has been in the press a lot as it has been implicated as a possible cause of 2 fatal crashes. The MCAS system was put in to prevent a wing stall caused by excessive Angle of Attack. My question is, outside of testing, has the system ever operated as intended and prevented a stall or approach to a stall?

If the system works as expected, how would even the average pilot know? Does the MCAS create any trace? How would anybody know without evaluating the FDR?

The MCAS system can make noticeable and pretty coarse control inputs as has been demonstrated in the 2 accidents @bogl.

Agree, but noticing the control interference checks only one of the boxes. Will the pilot file a report afterwards, and will he state that MCAS was helpful and that he could not have handled the near stall without it? I think that would be exceptional.

We don't know - until we hear about such a case!
A positive answer would require

a trace of MCAS action
sufficient evidence that the pilot could not have handled the (near) stall without MCAS.

This information could come from

a pilot who

notices the trim interference, and
perceives the situation as dangerous, and
reports the event

or

a flight data recorder that is analyzed, and

corrective MCAS action is found, and
it is evident from the data the pilot(s) did not / could not control the situation.

[ Am I missing any other way how MCAS could leave a trace? ]
A well-trained vigilant pilot can handle (near) stall situations in most cases.
MCAS is designed not only to get out of a stall, but to prevent the airplane from stalling in the first place. That means that
 the plane should never get into a critical stall situation, if MCAS does its preventive work.
All that just to say, it would be possible to answer "yes" as soon as there is knowledge of one averted incident, but it is impossible to conclude "no" from the absence of information.
I am very well aware that I wrote this theoretical answer while sitting in an arm chair, and I will happily remove it as soon as anybody with hands-on knowledge can provide more satisfying information.

Most airlines have a Flight Data Analysis section which uses the routine download of the FDR to automatically flag deviations from the normal flight profile for investigation.  The kind of maneuvering that would activate MCAS would vastly exceed the typical limits and be subject to a detailed investigation.  Most of the 737 Max FDR do have provision for discrete recording of automatic trim inputs from the FCC, which may or may not be MCAS, but the surrounding data will allow you tell MCAS apart from the normal automatic trim operation by the FCC.
The lines of communication between the operator and the NAA on information derived from this source are somewhat limited due to confidentiality provisions that pilot groups required in order to embrace this constant scrutiny of their daily work.

MCAS is designed only for extreme abnormal flight attitudes, normal activation would be rare. Activation of this sort is also likely to show on data logs and it seems likely that it may even set some an alert flag for the operation even if the pilot fails to report such an abnormal flight condition. Engines have been remotely monitored while in flight for many years(basic temp, pressure, and RPM), with some lag as it must traverse several layers of electronics and sat links.

1-Boeing wanted the system to be transparent, so presumably never reported. 2- Analysis of recorded data gives the actual AOA, but not the stalling AOA . Note that the stall alarm occurs well before the stalling AOA

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How does aircraft maintain precise speed, e.g. in formation flying or refueling?
I understand ailerons, elevators and rudders can be controlled to a very fine degree, and in precise flight, like formation flying, they can be used for very fine course adjustments to maintain the relative distance from another wingman.
But the throttle lever can regulate the thrust in range from near zero to several hundred kilonewtons by pushing it maybe 15cm forward. There's very little fine control to it and especially jet engines are sluggish to react to the changes.
How do pilots precisely fine-tune relative speed when traveling at high airspeed then? Are they using other tools - flaps, airbrakes maybe? Or am I underestimating the precision of the throttle, or missing some other mechanisms?

The key in holding the same speed as your wingman or the other aircraft is not to find the "perfect" throttle position, the key is to slightly adjust the throttle.
When you look at cockpit-videos of those formation pilots (like this - move the camera to the throttle, it's a 360-degree video), you can see that they are constantly moving the throttle. They almost never stick the throttle at one position. In that way, they can slightly adjust the speed and stay in formation with the wingman for a long time.
While flying in close formation at high speed, it's the same. Little adjustments of the throttle helps the pilot to keep the same speed as the wingman-aircraft. Flaps are not used in high-speed-flying because they can only operate below a maximum speed, otherwise they could get damaged. By using the air-brake, the handling of the aircraft changes, therefore the air-brake is not used very often while flying in formation.
tl;dr:
Skill

So the short answer is skill?

@Hollowy Yes, it's a combination of experience, feel for speed, training and many other things. All those together are 'skill'.

If you think about it, it's very similar to how you can hold a precise position against another car on the motorway if you wanted to - you are continually adjusting the speed using the accelerator. You maybe don't know how much you do it - it ends up being second nature.

@RoryAlsop: The difference is that at 100km/h, if you match your speed to 1%, you're moving 1km/h relative to the other car, which is a crawl Plus the only other thing to match is your yaw. If you do that at 1000km/h you need a 10x as high precision, while you match pitch, yaw and roll simultaneously.

@SF.: Which is part of why human-operated cars can be in much closer formations than human-operated airplanes. :-)

@T.J.Crowder That doesn't need to be the case. Just look how close, as example the blue angles, fly together through a looping.

@jklingler: As close as F1 leaders around a curve? I don't think so. :-)

@T.J.Crowder In this video, the Blue Angels are as close as six inches from each other.

@DanielR: Which is flipping cool (and bat---- crazy), and something like five inches more than F1 drivers sometimes come. :-) (Er, even when they don't end up actually colliding.)

And the combined number of people that could pilot either F1 or those aircraft to that precision with even a 10% chance of success is... what 500 world wide? Probably less!!

@corsiKa once you expand the list of candidates to include drivers in other tier 1 track races, and all of the national flight demonstration teams I suspect you'd be looking at more than 500 people who are doing it.  The pool of people who have the ability to do so if trained is almost certainly at least several times larger.  While not acrobatic, the number of military pilots who have to fly in tight formation for airborne refueling alone is probably in excess of 10,000.

@DanNeely Tight formation? Sure - 6 inches for aircraft and 1 inch for driving? I wouldn't think so. But I digress.

Still, consider consequences of an error. A gentle bump in F1 isn't disastrous. OTOH I remember stories about WW2 pilots, who, after running out of ammo, would flip V1 missiles with wing tips...

I call shennanigans! That Swiss F5 is on autopilot - there aren't any hands on the throttle or stick!!  ;)

@FreeMan Sure.. Formation autopilot...  :) If you look closely, you can see that it's a two-seater.

You can match speed and fly formation with another aircraft much in the same way that you can match speed and drive in tight proximity to another automobile on the freeway; just a stream of minute and precise inputs to the accelerator, steering wheel and brake pedal.  Aircraft have the additional challenge in that they move in three dimensions and their relative motions are much more inertial than an automobile; you cannot simply stop or arrest a relative closure as fast as you can in a car or truck.
Formation flying is an art form rarely practiced outside of the military because it is otherwise superfluous and useless in civilian aviation.  Training begins with two ship formations at 75-100 feet apart and gradually reduces to 15 or so feet as the student pilot builds ability and confidence in the maneuver.  Advanced formation flying or aerial refueling takes the student within 6-8 ft of another aircraft.  By this point, maintaining formation has become second nature but the student still has to refine the precision to the point that he/she can hold on the boom or hook up with the drogue basket.
Formation flying starts with a process of the wingman 'walking up' on the lead with a closing speed which gradually reduces the closer the wingman gets to the lead ship.  In general this is about 10kts for ever NM the two ships are separated by.  Once the pilot assumes formation, it's a matter of keeping your eyeballs glued on the leader and making minute stick and throttle inputs.  It just takes practice but you can get the hang of it within about 10-15 hours of practice formation flying.
There are limits to just how close you can fly next to another aircraft.  Precision flying teams such as the USAF Thunderbirds or the USN Blue Angels will never fly closer than a 36 inch separation between aircraft.  In addition this minimum spacing grows depending on the complexity and difficulty of the maneuvers which they are flying.

Saw an inaccuracy in this post. The Blue Angels fly 18 inches wingtip-to-canopy separation. Talk about precision!

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What is this aeroplane - not a Blackbird?
What is the aeroplane in the first image?
I noticed this photo in a youtube clip, and at first glance thought it was a three-engine Blackbird SR-71, but it appears to be a single-seater.

The text and audio does not reveal what the photo is of.

youtube.com/watch?v=nagVeYYt13s#t=10m41s

Some googling suggests that is a D-21 drone atop a M-21, and wikipedia has this somewhat-unhelpful photo.

That photo is from the Boeing Museum of Flight, in Seattle, WA.  Detailed description here: http://www.museumofflight.org/Exhibits/blackbird

@abelenky Nice find - thank you.  Shows a more useful photo,

The aircraft in the video is an M-21 and is actually a two place aircraft. One Pilot and one Launch Control Officer.

indeed. The rear windows are visible, albeit difficult to see due to the quality of the image.

The large aircraft is the Lockheed M-21 (which was developed from the Lockheed A-12, the same aircraft that the SR-71 was developed from), and the smaller aircraft is the D-21 drone.
The wikipedia article on the D-21 has a lot of information.

Deep Space thanks.  Apparently some editor has taken a rather amoeboid response to my answer. FYI the MD remark was humor!

It’s called an M-21 Blackbird.  It’s a derivative of the A-12/SR-71 family of aircraft modified for launching a supersonic ramjet powered reconnaissance drone called the D-21 (“M” designation standing for “Mothership” and “D” standing for “Daughtership”).  The program never worked out and destroyed one aircraft which the drone collided with during separation and launch tests.  The D-21 drones made several more flights, albeit by launching from a B-52 bomber using a rocket booster to accelerate it to Mach 3, but all but one flight failed, either crashing over enemy territory or sinking in the ocean either due to vehicle or telemetry failure.  The last known M-21 Blackbird is on display at Seattle’s Museum of Flight at KBFI.


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Are Lockheed Martin pilots considered civilian or military?
Came across this job on LM's website
https://www.lockheedmartinjobs.com/job/luke-air-force-base/f-35-instructor-pilot/694/10202293008#anchor-responsibilties
Since the organizations hiring you is a company, can a civilian aviator apply even of he or she has no background in any military capacity? Although chances are slim, is it not impossible to be hired for a military aircraft role?

There is a mismatch between the question in the title (pilot status) and the actual question (candidate experience).

Some of the requirements are:

Must have a minimum of 1000 hours experience in tactical fighter aircraft as a pilot.

and

Must have experience as a multi-ship flight lead in tactical fighter aircraft.

So yes, it is impossible to get this job as a civilian without any military fighter experience, although nothing stops you from applying, your application would be rejected as "not qualified".
As for the title question, LM pilots (those similar qualifications to the job posting) are civilian pilots (ex-military).

Top Aces have some tactical fighters in possession, including retired F-16. So that's where you could possibly get your experience https://robbreport.com/motors/aviation/first-privately-owned-f-16-fighter-jet-launch-1234614622/

For multi ship flight lead, consider airshow participation?

@Nederealm Not really, military aircraft repurposed for civilian uses aren't considered "tactical fighters". They are experimental exhibition category aircraft.

@Ron Beyer, a valid point from an administrative view, but irrelevant if the hiring manager decides that the experience is applicable.

@MichaelHall Usually these types of requirements come directly from the Government, and are not subject to "hiring manager" whims. They are hard requirements that cannot be adjusted.

@Ron Beyer, fair enough, but my point is that the difference between an F-16 "tactical fighter" and an F-16 "experimental exhibition" (minus actual combat experience with weapons...) is administrative in nature.  If a civilian test pilot had 1000 hours putting Falcons through their paces they would likely be competitive.

The F-18/F-18/A-4 pilots for these private companies also came out of the military. They don't just hire random civilian pilots (no matter how good) and train them on the -16s.

I know that.  99.99% of the time that is true.  It would be a very rare exception, but I do know a civilian test pilot with F-14 Tomcat pilot time in his logbook, so...

Technically you would be working for Lockheed Martin as a civilian in that role, but the job would almost certainly require former military experience as a fighter pilot, and especially as a former F-35 fighter pilot in one of the branches of service, preferably a former USAF IP.  Even tallying up the minimum items listed in the job description, you’re just not gonna compete with somebody who has the military credentials I described above.  The military experience with far outweigh any of the items listed in the job description for that role.


text:
Who makes the call to start in terrible weather conditions?
I once headed to the airport during a huge thunderstorm with winds above 55 knots and massive rain and some small hail. At the airport, I saw that most flights were delayed or even canceled. To my surprise, my flight was still planned to depart on time. At the counter, I got the information that it was up to the pilots to make the decision if they want to delay or if they what to depart during the storm.
My flight was only a short hop of about 50 minutes and given the direction of the storm it was pretty clear that the storm would reach the destination at the time of the scheduled arrival. And this is exactly what happened. It was the most turbulent, terrifying and scary flight I ever had.
In the last two days, there was another windstorm in Europe with winds above 60kts. The news reported that some airports were closed but there are also videos on Youtube about planes landing during that storm.
My question is: Is it really only up to the pilot to make this decision? Who else might make that call? The airline? The airport? Are there official rules about departing in such conditions?

As the question will still be valid and read in several years, you may precise dates when speaking of "the last two days"

@ManuH The date of the post is clearly visible if someone wants to figure it out several years from now, and this specific event (Storm Ciara / Sabine) is not really at the heart of the question.

Who else might make that call? The airline?

Yes, if the airline thinks the weather is too bad at a particular airport for safe operations, it can just cancel all flights from that airport without asking the pilots.

The airport?

If the airport closes completely, then it is closed. No flights can depart any more, even if the pilots consider it safe.

Is it really only up to the pilot to make this decision?

If neither the airline cancelled the flight nor the airport has closed, it is indeed up to the pilots, or more specifically to the PIC (Pilot In Command, the Captain on an airline flight). They are ultimately responsible for the safe operation of the aircraft and have to make the decision:

4.5.1 The pilot-in-command shall be responsible for the safety of all crew members, passengers and cargo on board when
  the doors are closed. The pilot-in-command shall also be responsible for the operation and safety of the aeroplane from the
  moment the aeroplane is ready to move for the purpose of taking off until the moment it finally comes to rest at the end of the
  flight and the engine(s) used as primary propulsion units are shut down.

(ICAO Annex 6 Part 1 - 4.5 Duties of pilot-in-command)
The SIC (Second In Command) also gets a say in this because of crew resource management, meaning if they think it is unsafe to depart, they can and should speak up.

Are there official rules about departing in such conditions?

The respective national aviation authority may have rules on when a departure is permitted, but this will depend on the exact location. The pilots will however have received rules and training from their airline, which should indicate when a departure is allowed. The most important aspect to consider are the aircraft limitations. There is no legal crosswind limit for a takeoff, but e.g. the Boeing 737 FCOM lists a demonstrated value:

The maximum demonstrated takeoff and landing crosswind is 33 knots.

(Boeing 737 NG FCOMv1 1.10.2 Limitations - Operating Limitations)
It would be considered unsafe to depart with a stronger crosswind.
Note that limitations for landing are typically stricter than for departure and the pilots are legally required to check the expected weather at the destination airport before departing.
In Europe, Eurocontrol can also delay a departure due to expected weather en-route or at the destination airport. See What is the difference between en-route delays and airport delays?.

Good point on the CRM factor - the Pilot Not Flying should feel empowered to speak up if they don't believe continuing with the take off is a prudent thing to do.

It should be pointed out that the pilots, although they have the final authority of making the decision, will never (as I think should be happening) take a risky desicion which will break the rules of the limitations given by Boeing or the company which also has the authority to make its rules of operation more restrictive but never less restrictive.
For example, unfortunately, in this last accident with Pegasus (although the investigation is not over yet of course), the pilots landed with winds of 22 gust 30, almost complete tailwind. First- it's almost past the limitation (15 tail).

Second- the pilots could have taken a decision not to attempt a landing in this situation at all, and nobody would have judged them for the worst.
In the end, it's a matter of the Captain's judgment exactly in those cases where it's not past the limit but will definitely be a nonsafe landing/takeoff- and that is exactly his job because the tower won't stop you from making mistakes all the time, it's not their life on the stake with the gusts pushing them off the runway.

At the end of the day, the final authority on making, or not making the flight has to rest with the pilot. If you reverse the question, and a pilot thought that it wasn't safe to go, but there was an outside force saying they had to go, that wouldn't be ideal either.
Since you didn't mention specifics, there isn't a way to dig into other specifics, but airlines, charter operators, flight departments, etc, may have published (often just internally - they don't share these), established Standard Operating Procedures (SOPs) that have guidelines regarding visibility and wind speed, runway conditions, etc, that must be at or better than in order to take off, but even in that there is a level of subjectivity to the decision to take off.
If we look to the FAA, the guidance is in 14 CFR 121.651 (I know your question mentioned Europe, but it's probably pretty similar). It really doesn't talk about wind, just visibility. You have to be able to see at least parts of the runway environment.
Depending on the aircraft, there might be other considerations: maximum demonstrated crosswind, for example.
You don't really know what it's going to be like until you're in it, and pilots seem to be pretty optimistic people. So, if the weather data is stale, and the storm looks like it's moving through on radar, then there is a pull to make the flight.
So to answer your question: there may be Standard Operating Procedures or airframe limitations (crosswind, etc), but if those aren't a factor, the final call is up to the pilot.


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How much does it cost to ground a B737 max aircraft for an airline?
What are the cost items for which an operator with such an aircraft in the fleet incurs per aircraft because of the grounding of the Boeing 737 max aircrafts and how much is the average cost incurred?
Is there any possibility of claiming the losses by the airline companies from the Boeing company?

I am guessing that the cost is actually not the big problem. I expect loss of revenue to dwarf the costs by orders of magnitude. You need to pay for parking, and that's pretty much it.

Well we can look at another grounding case to see what it costs.
Boeing grounded the 787 Dreamliner. This grounding lasted about 90 days (at least as of the estimated costs by ANA, I think the actual grounding lasted about 116 days).
Japanese carrier ANA had the largest 787 fleet at the time with 17 of the 51 in operation estimated it's costs at $15 million.
Doing some simple math, \$15,000,000 for 17 aircraft works out to be about \$882,352 per aircraft for the 90 day grounding. This is about $9,800 per day/aircraft.
They also estimated that this resulted in ¥1.4 billion in lost revenue. This is \$12.7m USD (in today's dollars). That gives a lost revenue of about $3320 per seat, per day (averaging 250 seats per aircraft).
Now taking into account that there are 393 737 MAX aircraft as of the grounding, with an average seating of around 190 passengers, this could cost airlines significantly. Just in terms of costs, extrapolating the 787 numbers and assuming they are grounded for 6 months, looking at about half a billion dollars (*assuming the costs for grounding the 737 are 75% of the 787 in terms of storage and maintenance) for the entire industry.
In terms of lost passenger revenue, we can assume the numbers are about on par with the 787 since it is a more heavily utilized aircraft (shorter routes, more flights/day). Using the same 787 numbers we would be looking at about $44.6 billion dollars, again, industry wide (and yes, this number seems extremely high to me, but working from what ANA claims).
Can they claim this cost for Boeing? Maybe. They may be able to recover the costs of storing and maintaining the aircraft during the grounding. It is unlikely that they would be able to recover the lost revenue (and it would put Boeing out of business to do so). We'll have to see when this all washes out what the airlines do with Boeing. Most likely they will negotiate deals with Boeing for preferential pricing on future aircraft or some other kind of cost-offsetting deal.

Is your "44.6 trillion dollars" supposed to be Yen?

@8one6 No, it is USD. 3320 USD per seat, per day. Averaging 190 seats for the 737 that is 630,800 per aircraft, per day, times 393 aircraft is 247,904,400 USD per day for the entire fleet. Multiply by 180 days (estimated) and you get 44.6 trillion USD. It seems high to me, yes. I'd guess that the number is closer to $1000 per seat, which would still be more than $14 trillion USD.

What am I missing....247mm * 180 = 44bn, not 44tn, right?

My brain is on weekend mode...

The 3320 USD lost revenue per seat sounds excessively high. The 787 aircraft would only fly a leg or two per day meaning an average ticket price of at least $1660, a very expensive ticket...

To answer the second part, airliners come with all sorts of warranties. This is because any small problem on an aircraft easily can reach into the tens to hundreds of thousands of dollars.  This makes it economic to get lawyers involved and sue, so both sides have incentives to write down everything that likely goes wrong and agree on appropriate compensation as part of the purchase contract.
That way, when an issue occurs, they'll be more likely to pull out the contract and figure out what is owed, rather than fight over it in the courts.
The applicable warranty for groundings would be a dispatch warranty that says that cancelled flights due to technical reasons are less than some percent, or else $X will be paid per cancelled flight over the limit.
These details are proprietary and negotiated with each customer, so it is difficult to know what $X is, which may vary by customer as well. A typical contract is here, filed with the SEC. You can see that Airbus does provide a "DISPATCH RELIABILITY GUARANTEE" but that's pretty much all that is known publicly.
A separate warranty of airworthiness would cover the costs for any repairs. Those are much simpler: the airframer would provide a credit for the cost of parts, plus an amount per labor hour.


text:
What are the climb rates during the different phases of flight of an A320?
I have read about common climb rates for an A320. It is said that the initial climb rate for an A320 is between 15-20° and it differs depending on the weight and also the altitude.
I therefore have the following questions:

Do climb rates for a given flight mission stay constant in one phase of flight (e.g. until reaching 1500ft altitude) and then change at a specific flight level or are they continuously adjusted?
Do given climb rates exist for (one arbitrary) given flight mission?
Is there a method to calculate the change of climb rates depending on altitude and weight?
Are there sources like papers, reports, manuals that will work for genuine citation?

Usually you aim for climb speeds, the rates vary with air density and other factors.

If I'm not mistaken, 15-20° is a climb angle. The rate of climb would be measured in feet-per-minute, not degrees, and would depend on things like pitch angle, flap settings, throttle settings, and air density.

Barring restrictions from ATC, aircraft generally climb as fast as possible. That means setting engines to standard climb setting, pitching the nose to maintain best rate of climb speed (speed at which drag is lowest; in Airbus also known as “green dot speed”) and the rate of climb is whatever it is. Since engine thrust decreases with altitude (with air density, actually), so does the rate of climb.

I will attempt an answer, although the question is a bit unclear. Climb rate is not measured in degrees or any other angle measurement unit. It's altitude per time unit (feet per minute usually). What you are mentioning is the climb gradient. See relevant question for details
Now regarding your questions:

Do climb rates for a given flight mission stay constant in one phase of flight (e.g. until reaching 1500ft altitude) and then change
  at a specific flight level or are they continuously adjusted?

Depends on what the pilot wants to achieve. Do they have to meet a restriction? Noise abatement, crossing etc? Are they instructed by ATC to climb quicker (if able) or slower to maintain separation with an opposite or crossing flight? In any case they have to adjust their climb rate.

Do given climb rates exist for (one arbitrary) given flight mission?

Yes and no. Given by whom? The manufacturer? The airline company? The regulations? If the SID you've been assigned has climb restrictions imposed, then you have them given but not a firm number. It's usually less than or more than (or both).
Also have in mind that climb rate is affected by aircraft weight as you can see in the document that I've linked below. But this is more of a limit rather than a given rate for the specific flight.

Is there a method to calculate the change of climb rates depending on altitude and weight?

Again, on whose perspective? The aerospace engineer's who designs the plane? Or the pilot's who will "just" fly it? In the second case there are lookup tables, but I hardly recall details since it's been almost 10 years from the last time I've seen one.

Are there sources like papers, reports, manuals that will work for genuine citation?

Your best bet is BADA. You might want to have a look into this document * where it actually describes (among others) the climb rates for various altitudes and weights for several aircraft types.
Note that this is quite an  old document dated back to 1998, but I would guess this is the best one can get since BADA is proprietary and has lots of use restrictions. So I wouldn't expect anything much newer to be publicly available.
* (labeled BADA Aircraft Performance Summary Tables since links have the bad habit to disappear)

According to the EUROCONTROL Performance Database, the usual climb rates and speeds for an A320, for ATM purposes, are those depicted on the image below:

Source: https://contentzone.eurocontrol.int/aircraftperformance/details.aspx?ICAO=A320&ICAOFilter=a320
Note that rate of climb (ROC) is given in feet per minute, not degrees. If measuring degrees, you are talking about the climb gradient, not climb rate.


text:
I'm trying to replace the Colomban CRI CRI engines with twin 72v 3000w dc electric motor. Will the plane fly?
This is the 72V 300W DC motor:

(source)

Those are only 4 hp. I think you need a bit more juice to fly a Cri-Cri than 8 hp.  The original's engines total 30 hp.  You need two 12 Kw motors.  You need to then figure out where to put the batteries  such that if they catch fire you won't turn into a roman candle.  And once you have the thing all installed with the same all-up weight as the original, you'll find out your endurance is only about 1/3rd of the gas version.  At this stage, electric power is really only practical for motor gliders unless you can live with the very short range.

@JohnK, this reads like a good answer...

I think I'll classify the Cri-Cri as a 'wearable airplane'

Electric motor power ratings aren't quite the same as gasoline engine ratings -- in general, a 2 HP electric motor will do what a 4-5 HP gasoline engine will do -- but you're still underpowered here with two of these and a 2x conversion factor.

@Zeiss Ikon, what if I should use 6000W motor each?

@BenFabulous That would give you 16 hp electric, roughly equivalent to the original engines on the Cri Cri -- but they'll weigh more and suck down batteries at least twice as fast as the 3 KW motors -- you might wind up with barely enough run time to take off, go around the pattern, shoot a touch and go, and go back around to land.

Those motors are only 4 hp each. I think you need a bit more juice to fly a Cri-Cri than 8 hp. The original's engines totaled 30 hp. Which means you need two 12 Kw motors. You need to then figure out where to put the batteries such that if they catch fire you won't turn into a roman candle.
And once you have the motors and controllers and batteries and the fireproof battery enclosures all installed with the same all-up weight as the original, you'll find out your endurance is only about 1/3rd of the gas version. At this stage, electric power is really only practical for motor gliders unless you can live with the very short range

There is an electric Cri-Cri but I can't find specs on its (4) counter-rotating electric motors or battery capacity.

They're probably about 6-7 Kw each you would think  Reading down the article it sounds like it has an endurance of about an hour, about what I would expect.  You can't really go anywhere, but to just go out and frolic in the sky for 20 minutes, that would be fine. One of the more impressive electric developments I've seen lately is the Open PPG SP140 paramotor.  Makes 160lb of thrust and runs for an hour, not too bad for a paramotor, and only 7 grand complete except for the wing.


text:
Could "Mimiron's Head" or "flying machine" fly in the real world?
Mimiron's head is an endgame raid reward from the game World of Warcraft that's basically a cup with an upwards rotor mounted on the rear and 2 side rotors pointed downwards.

 is a video which shows what it looks like.

 shows it flying around with a pilot.
The Flying Machine, and the upgraded version Turbo-Charged Flying Machine, is a mount that a player can create themselves using the Engineering profession. It looks more like a traditional helicopter, but instead of a rear-mounted rotor, it has an engine with a propeller on each side.

 shows the Turbo-charged Flying Machine flying around.
now, to me as an aviation-illiterate person, it looks like as-is, either mount could not quite work in the real world, but if you made some modifications, they could work. Is this true? Could you make these helicopter-like vehicles work in the real world? Assume current technology or immediate-future technology (available in the next 5 years).

It wouldn't fly well. Unless the CoG is between the center thrusters and the rear rotor, it would tip forward and crash immediately. It looks like the CoG is likely forward of the thrusters in the center, so bad news for the pilot. Unless, of course, the center thrusters could lift the entire weight on their own and the rear rotor had variable pitch that could go negative in order to provide pitch authority to keep the nose level.

Could they fly... ...Maybe
The second device looks quite a bit like an Auto Gyro which is very much capable of flight.
The first device looks like (as has been mentioned) the center of gravity would be an issue. If those side pods generated enough thrust along with the main rotor you could get it off the ground however I would think it would be very hard to control.

To say nothing of the off-center connection on the shaft for the main rotor. Vibration much?

With enough thrust anything can fly, as rockets had proved

@Jean rockets carefully balance their thrust with the centre of gravity though.

@jean   With enough thrust, but also _ with enough control _

The craft won't be able to fly without addressing some serious balancing issues. Both have their rotors far away from the centre of gravity, and this can only be compensated by the rotors if they exert a high torque, by a fixed rotor head. Which will then create serious controllability issues, since there is no way to input cyclic and collective control.


text:
When communicating altitude with a '9' in it, should it be pronounced "nine hundred" or "niner hundred"?
It sounds a little odd, but trying to understand if that's the recommended way to communicate.
E.g. 9900
"Nine-thousand-nine-hundred"
vs
"Niner-thousand-niner-hundred"

In the UK, the RT rules for the ANO are in Cap 413 and section 2.13.2 states:

All numbers used in the transmission of altitude, height, cloud
  height, visibility and runway visual range information which contain
  whole hundreds and whole thousands shall be transmitted by pronouncing
  each digit in the number of hundreds or thousands followed by the word
  HUNDRED or TOUSAND as appropriate. Combinations of thousands and whole
  hundreds shall be transmitted by pronouncing each digit in the number
  of thousands followed by the word TOUSAND and the number of hundreds
  followed by the word HUNDRED; examples of this convention are as
  follows:
Table 5
Number    Transmitted as              Pronounced as
10        One Zero                    WUN ZERO
100       One Hundred                 WUN HUN DRED
2 500     Two Thousand Five Hundred   TOO TOUSAND FIFE HUNDRED
11 000    One One Thousand            WUN WUN TOUSAND
25 000    Two Five Thousand           TOO FIFE TOUSAND

There isn't a specific example of NINER here, but given that the examples do actually use their prescribed pronounciations, you'd expect NINER to be used too.
I can't remember hearing it but the other conventions seem to be adhered to by professional pilots in the UK (we Sunday afternoon bimblers are not as good at it).  Non-native english speakers are very exact in their use of the published pronounciation
No doubt there will be a professional along in a minute, who can give you a more authoritative answer
EDIT: The reason I can't remember hearing "Niner-thousand-niner-hundred" may be because, in the UK, it would be above the transition level?

Several numbers are not pronounced the way they are in English. Niner is the most obvious and most US pilots use it. In my experience, tree and fife are heard less often. I don’t recall ever hearing anyone say fower.
From Wikipedia

The NATO phonetic alphabet, officially denoted as the International
  Radiotelephony Spelling Alphabet, and also commonly known as the ICAO
  phonetic alphabet, and in a variation also known officially as the ITU
  phonetic alphabet and figure code, is the most widely used
  radiotelephone spelling alphabet.

ATC should always use the correct pronunciation and phraseology.  Pilots aren't as consistent, at least if they're native English speakers; as long as we're understood (the primary goal of communication), we can get away with a lot of shortcuts.
In the US, NINER THOUSAND is used by most pilots, but you'll hear NINE occasionally.  NINER HUNDRED doesn't come up often since we usually fly at multiples of 500 feet, but I'd expect the same tendency when it does.
I've never noticed US pilots using TREE, FOWER, FIFE or TOUSAND, though.  Unlike NINER, those aren't easily distinguished unless you're listening for them specifically.  They seem to be used mainly by pilots whose native languages don't have the sounds necessary for the normal English versions.

NINER is an artifact of the "phwa phwa phwa bwa bwa what-the-hell-did-he-say" days of radio telephony, with vacuum tube equipment and carbon microphones and raspy, garbled, muffled audio, to prevent it from being mistaken for the number five.
With the FM radio quality audio of modern avionics, it's not really required any more and sometimes you hear it and sometimes you don't.  No controller will scold you for saying nine instead of niner.

What about HF as is sometimes used in oceanic ATC?  Or noisy cockpits, or bad microphones, or mumble-mouth speakers, or thick accents?

In that case you will use NINER.   It'll be obvious when it's necessary.

Please see Why do English-speaking pilots and ATC say “Niner” instead of “Nine”?


text:
Canceled regulations for an STC CCL
easy question: When creating a list of regulations (and the documents that show compliance with those regulations) that apply to our STC, if one of them has been canceled, would we continue to use that regulation+Amdt basis or the successor regulation?
The install is assumed to be non-significant based on 14 CFR 21.101, so we're using the cert basis on the TCDS.

Until you discuss your change with DAR or FAA, any assumption is a risk factor. Have you followed 21.101-1B - Establishing the Certification Basis of Changed Aeronautical Products?  You need to make a solid case to the FAA that using the 'old' rules is adequate.  If you can't, you will need to comply with the current rules.  It's typically not a simple yes or no, unless you choose to use the new rules.

@Gerry thanks, I agree that there is risk until we apply, I'm not asking about determining certification basis via 21.101, I'm specifically interested in understanding if what's on the TCDS can be used if it contains regulations which have been canceled. I agree that we will need to either comply with latest regulations or provide an argument as to why we will not be able to do so if we've been found to be significant by the FAA after we submit the PSCP.

I agree this is for the DAR or FAA staff to answer.

There are two possible results. You will either need to comply with the current rules or you can use the certification basis that defines the aircraft's current configuration. That basis is defined in the TCDS and any applicable existing STCs. Those STCs may be the same as the TCDS or they could be to rules newer than the TCDS but not necessarily current. If you're using the original cert basis and it includes rules that have been rescinded/superseded, that's acceptable. That's kind of the point of the whole discussion.

Since you mention the PSCP, I'll point out that that is the vehicle for negotiating the plan with the FAA. It's not a case of "Here's my plan." Every one I've dealt with was multiple drafts back and forth until we had a plan that was approved. The cert basis was a big part of that negotiation.


text:
If the 10000ft pointer is reading 5 (50000ft) when you are at 10ft how do you get it back to zero
Kollsman altimeters 10000ft pointer adjustment

@CrossRoads Please don't answer in comments.  If you have an answer, make it an answer.  Comments are for clarification (which this question needs).

Check that nothing is causing suction on the static port system, low pressure will cause a higher altitude reading. If the static system is functioning, then turn the knob counterclockwise to read the correct pressure, it is probably off by quite a bit. If it has the correct pressure, then the altimeter likely needs servicing.

If the altimeter is showing 50,000' while the aircraft is off, the altimeter is bad. If it only shows 50,000' after the aircraft is started, there is probably a plug in the static system. I would also have them open the alternate static and see if that works, if it does then the static system is plugged, otherwise it's probably time for a new altimeter.


text:
What does ATC mean when they say "no longer a factor"?
During radar vectors, the ATCo informed to the pilot, "no longer a factor." Please, can you clarify to me what this radio transmission means?

Are answers that discuss the meaning of a phrase in general on-topic here? I thought I was in ELL for a moment and I wrote up an answer discussing the meaning in general, and then I realized I wasn't after I posted it, so I deleted it.

What does the acronym "RT" stand for? I don't think I've ever heard that before.

@TerranSwett "Radiotelephony."

I assume the o in ATCo is for operator? I thought ATC was either Air Traffic Control or Air Traffic Controller, depending on context.

@CGCampbell the term in the United States is "Air Traffic Control Specialist." Most of the rest of the world uses "Air Traffic Control Officer."

This one is usually replied in relation to other air traffic around a particular flight which at one point may have posed a collision risk but is no longer in a position to do so.  Example
ATC: “United 2410, traffic is two miles at your ten o’clock at 5,700.  Cessna.  Report them in sight.”
If it appears the other aircraft will no longer cross paths with the aircraft being directed, the controller may say something like:
ATC: “United 2410, the Cessna traffic no longer a factor.  Turn right heading 340.  Descend and maintain 3,800, slow to 160 knots.”

ATC typically wouldn't specify direction and distance when saying traffic is no longer a factor (what's the point?). Just something like "mentioned traffic no longer a factor".

It means that the previously mentioned traffic is no longer likely to cause a collision, and that the two aircraft in question are now on diverging flight paths. In layman's terms, it tells the pilot to stop worrying about looking for the other traffic.
"Cessna 3AB, previous traffic no longer a factor."

Or, less commonly, "Cessna 3AB, if you are receiving this transmission, previous traffic no longer a factor."


text:
Is there any difference between "EMERGENCY LANDING" and "FORCED LANDING"?
Emergency landings and/or forced landings are stressful situations, but talking about meanings, are they the same, please?

Not all forced landings are emergencies, and not all emergencies are forced landings! (See below)
In general, the term "Emergency Landing" is a superset which covers a bunch of different scenarios where a landing is not quite to plan. Such as

Forced landing due to mechanical failure. Note that a forced landing can absolutely be at an airfield. It can also be in a literal field.
Precautionary landing, such as where continued flight is possible but inadvisable
Ditching in a body of water
Belly landing due to inoperable landing gear

A forced landing can also be one where the pilot is forced to land due to military interception, which is not always an emergency.
This is all covered in great detail here

The FAA also publish some useful information on this subject which repeats much of the above information, reproduced below for clarity

Types of Emergency Landings
The different types of emergency landings are defined as
follows:
• Forced landing—an immediate landing, on or off an
airport, necessitated by the inability to continue further
flight. A typical example of which is an airplane forced
down by engine failure.
• Precautionary landing—a premeditated landing, on
or off an airport, when further flight is possible but
inadvisable. Examples of conditions that may call for
a precautionary landing include deteriorating weather,
being lost, fuel shortage, and gradually developing
engine trouble.
• Ditching—a forced or precautionary landing on water

In the UK Forced Landing = Emergency Landing

@GdD I'd like to see some source for that, it would make a good addition to this answer. In 20 years of flying in the UK, I'm not sure I've seen any official definitions

@GdD Also, as my first sentence alludes to, there has been the occasional military interception which force a landing at stansted (usually) which are not emergencies. So not all forced landings = emergency landings. The terms are used fairly interchangably - does not mean that they are the exact same thing.

I've only heard "forced landing" synonymous as an unscheduled landing without power. e.g. PFL. I wouldn't consider an enforced landing by somebody to be a "forced landing" in this context.

I sort of agree, I've only heard it used in the same context. But, that's not what ICAO says. Interested in any sources other than "Thats what I always thought"


text:
What's the difference between Holding Point and Hold Short?
I heard some ATCos requesting pilots to report, on holding point, and also hold short. Is there any difference on them?

The holding point is usually a fix in the STAR where aircraft are "held" flying a pre-defined radial for traffic congestion purposes; and I have only heard it in context of ATC referring to aircraft flying.
Holding short is very important. It means stopping before entering a runway area and is marked by two solid lines. You should hold short (ie, before) the solid lines.
Here is a picture of an aircraft that is stopped short (source: google maps of OMDB):

The lines are marked as two solid lines, followed by dashed lines; the holding side is on the solid lines:

(Source: propilotmag.com)
The holding position however, is a place on the ground where aircraft are to report once they taxi to it.
From the OMDB AIP:

Red inset lights supplemented with elevated lights on either side of
  the holding position. Runway holding positions (CAT I and CAT II /
  III) and intermediate holding positions for general service road
  crossings are provided with Stop Bar Lighting.
RWY Guard Lights: RWY holding positions are provided with a pair of
  yellow flashing lights on either side of the Stop bar
Intermediate Holding Position Lights: A set of three amber lights or
  full red stop bar are provided at intermediate TWY holding positions.

Source : DCGA Website
Further on the same page:

2.20.5.2.2 Pilots in receipt of a conditional line-up clearance on a preceding departing aircraft shall remain behind the subject aircraft
  but may cross the runway holding point, subject to no illuminated red
  stop bar and then enter the runway upon receipt of the clearance.
  There is no requirement for the subject aircraft to have commenced
  take-off roll before entering the runway. Pilots must be aware that
  there may be a blast hazard as the aircraft on the runway applies
  power.

However, ATC may give an instruction on the ground such as:

November 5 Bravo, taxi to holding point Charlie Runway 30R

This usually refers to a physical holding position.


text:
Is there any technical word to be used on Radio Telephony, to say that there is a "body air-shipped"?
A great number of dead bodies are transported by airplanes everyday.
How will pilots report to ATC they are transporting it/them?

Why would they mention it to ATC? In case of a passenger plane the number of passengers could be mentioned as (number) PAX, everything else is cargo. And as far as i know cargo is never specified to ATC.

For sure, as an ATCo, I had to deal with that, as the destination was closed, and they alternated an airport without this structure to support it.

Not a dupe but related

A relevant discussion on Pprune. Particularly relevant for Search-and-Rescue (SAR) and medical operations.

The crew needs to be advised primarily, usually via the NOTOC(Notice to Captain) as this falls under Dangerous Goods classified as HUM under IATA.
But indeed, the controllers are not made aware of it, nor is it mentioned in the flight plan( as far as I'm aware).

In the US, pilots may use the term "FALLEN HERO" to indicate they are transporting remains of military servicemembers and ATC will attempt to provide priority handling in accordance with the 7110.65 2–1–4q. This is the last in a long line of operational priorities, indicating treat better than simply "first-come first-served" but below any other conflicting priority.
Civilian pilots may use the term "MEDEVAC" or the now-archaic "LIFEGUARD" to indicate a request for priority when on an active air ambulance mission (I believe the terms "AIR EVAC" and "HOSP" are used by the military). These flights are afforded very high priority, second only to aircraft in distress. The term may be used when carrying patients or when carrying time-sensitive supplies or equipment, for example a donated organ or medicines.
To my knowledge there is no phraseology used to inform ATC there is a dead body on board. If there was a need for ATC to know about it (for example, the body is unexpectedly dead and the flight will need to be met by medical personnel) the pilot would use plain English.


text:
What is this fuselage-side aerial used for?
(instagram.com)
I have seen this picture, and this feature on the port fuselage called my attention. Does anybody know the purpose of this?


text:
Effect of Rudder on Velocity Vector
Suppose we have an aircraft flying in steady, level flight at zero angle of attack. In this configuration, the velocity vector $\vec{V}$ is perfectly aligned with the $x$ axis. At some time $t=t_0$, the pilot applies a finite positive rudder input $\delta_{r}$ which produces a yawing moment on the aircraft. My question is what will happen to the velocity vector immediately after the rudder input gets in.
From my understanding, as soon as the the pilot inputs the rudder, the plane produces a positive side force (in the $y$ direction), which causes a negative moment about the $z$ direction. We can write this as something like $N = -l_vY_v$, where $l_v$ is the distance from the vertical tail to the CG, and $Y_v = C_{L_v}Q_vS_v$ is the side force as mentioned above. We can write this in non-dimensional form as the yaw moment coefficient, i.e.
\begin{equation}
C_n \equiv \frac{N}{Q_wSb} = -\eta_vV_v\frac{\partial C_L}{\partial\delta_r}\delta_r,
\end{equation}
where $\eta_v = Q_v/Q_w$ and $V_v = l_vS_v/(Sb)$. So, a positive rudder deflection will give a negative yaw moment, as seen in that equation, proportional to $C_{L_{\delta_r}}$. However, this doesn't tell me anything about the velocity vector. Intuitively, I would think that after a long time when the aircraft has time to stabilize itself, the velocity vector would point along some angle $\beta$ from the $x$-axis relative to where to was before. However, I am not sure what would happen immediately. Maybe there is an immediate sideslip angle, and over time it decreases (assuming the aircraft is stable). Thanks for the help in advance!

Immediately, the only unbalanced force is $Y_v$.

The yaw will produce an angular acceleration about the z axis, thus an angular velocity, and the yaw will produce an induced roll angular acceleration, thus an angular velocity.   Compared to the moving coordinates  of the plane the velocity stays in the x axis mainly, but the velocity, with respect to a fixed coordinates system on the earth, will be changing direction.


text:
How is heading / windspeed written?
You have been given wind direction and speed, how would it be expressed?
Thanks

You need to clarify this, when are you writing it? Who is giving it to you? What do you need it for? Usually when listening to ATIS I write it down like "310 @ 12", or "310 @12G15" if there is a gust, each pilot develops their own short-hand for instructions...

Dang, really?  This was put on hold in 2 hours, but I think it could be easily edited and answered even if that means giving more information than the asker is seeking.  Metars, TAFs, ATISs, etc. & then there's winds aloft.  Anything missing?

@RyanMortensen WIthout editing this its impossible to know what the OP was asking, however if you think that you can make a new question with information relevant to the community, by all means make a new question and you can even answer it, its encouraged here.

@RonBeyer touche` sir!  I didn't look at the edit history.  Someone inferred enough in the first edit to make the actual question appear to be obvious, but looking at the original form this question just needs plain deletion.

From your original question before the edit, we always express wind direction as where it is coming from.

Simon answered the original question perfectly. I see no reason for such monumental edits or closing the question.

@Simon: If this is the actual question (that's not clear to me), then it's a duplicate.


text:
How do you reconcile an airline flight number with an ADS-B record, is this possible?
If you go look at arriving flights at an airport, you'll see something like "American Airlines Flight 224."
How do you cross reference that ADS-B flight data?  Is this possible?  Seems like there's some information in the "Call" field but it's not enough to match up the flights.

If you can get the tail number (N-Number), you can look up the aircraft registration to get the Mode-S code. It isn't clear to me what "ADS-B" data you are talking about? Where do you get the ADS-B data from?

The Aircraft Identification Field (ACID) has the flight ID which can be correlated to the flight number. You have to have a lookup table that is up to date. I think there are various website that maintain such a table.

@RonBeyer i'm getting data from http://www.adsbexchange.com/ and I'm trying to cross reference ads-b data to flight numbers published by airlines.

@DeltaLima here's a data sample from ADS-B, I don't see any aircraft id field, is "Call" what you're referring to? https://gist.github.com/kevinchugh/d6af1f736f33351e1820fb4d8e52bf5c

Hi Kevin, yes the ACID is called 'Call' there. You can use that for looking up the flight number.

UAL1001 is the flight number. It's the number for a regularly scheduled flight from Quito, Ecuador to Houston, Texas.


text:
What makes the "howling" sound from airliners?
Quite often I hear a kind of "howling" sound coming from airliners when I'm at a general aviation airport, which is located at 13nm from an international airport.
Normally these airliners overfly the general aviation VOR at around 10.000ft and then keep descending while flying towards the international airport.
Does anyone have any ideas about what could be the cause of such a weird noise? Could it be associated with any aerodynamic effect?

It is probably low speed engine noise. If you are 13nm from the airport, the aircraft are probably quite a bit lower than 10,000 feet.

I live in the glidepath of DIA's southern approach and I think we're hearing the same thing.  It sounds like the pitch of the engine changes, like how the sound changes as you blow over a straw that is dripping water.  I don't know how else to describe it, and I've thought about sitting outside with my phone recording in hopes of catching it.

If the airplanes in question are BA-406s then it could be flap deployment, they make a weird noise when they are extended.

I've just been told that spoilers could be the cause of the noise, as they are deployed they destroy the boundary layer, making the howling sound. Could that theory be the correct one?

I thought the howling noise was passengers looking for their luggage in Denver ... :-)


text:
Does the main helicopter rotor blade shape affect noise?
Most blades are squared off at the end. The Cobra fighting ship has pointed tips. Does this cancel out the "wop wop" noise? The reason I ask is that today I saw the Cobra in this news article. The tips are pointed. In 1968 I worked at Bell Aerospace making blades for use on Hueys and all had squared off tips as were tail rotors. Seeing this bird brought back memories.

Yes. Especially tip shape, which is optimized in most modern helicopters (and upgraded older ones) to reduce noise.
Basically, the blade tip shapes are optimized to reduce the noise caused due to blade-vortex interaction (BVI). From Parametric Study for the low BVI Noise BERP Blade:

The BVI (Blade Vortex Interaction) phenomenon,especially parallel interactions between the helicopter main rotor blade and the tip vortex, is the cause of significant noise and vibration problems in helicopter operation. In particular, the descent  and banked  turn  flight  conditions  are known to produce significant BVI.

This phenomenon is explained in this article in rotorandwing:

... higher-pressure air will spill out from under a rotor blade at the tip, get sucked toward its upper surface, and create a strong corkscrewing swirl of air, or tip vortex. ... an approaching blade will often come into the vicinity of a tip vortex left by a preceding blade. When the high-energy swirling air strikes the rotor blade, it causes a sudden change in angle of attack and an associated change in pressure on the surface of the blade. This is what creates the loud impulsive noise that can be annoying to those on the ground.

If the blades are designed in such away that the pressure change due to the BVI is reduced, the noise can be reduced. This is the reason for the differing shapes of modern helicopter blade tips. A good example is the Eurocopter Blue Edge concept, which Airbus claims reduces noise by 3-4 dB:

Blue Edge™ main rotor blade has a double-swept shape to change the blade-vortex interaction (BVI) that occurs at the tip of any helicopter blade – significantly reducing noise levels created during a typical descent profile.
This ... noise reduction technology has been validated ... flight trials using a five-blade Blue Edge™ main rotor on an EC155, showing a 3-4 dB noise reduction.

Eurocopter Blue Edge Wing; image from wired.com
That varying the tip shape will affect the BVI and consequently noise, was well known (for example, see the NASA paper Evaluation of Helicopter Noise Due to Blade-vortex  Interaction for Five Tip Configurations by Danny R. Hoad, which compares the sound produced by various tip shapes). However, with the advances in computer modeling and CFD, a number of modern helicopters incorporate blade tips that have been designed with the express purpose of reducing BVI and noise.


text:
Can a person with a tibia problem become an air traffic controller?
I have a healing tibia. In the worst possible case, if it does not heal fully, will this impede a future attempt to become an air traffic controller?

In what country?

In the US, an air traffic controller is required to have Class-II medical. However, it is mentioned here that:

The applicant must have no deformity of spine or limbs of sufficient
  degree to interfere with the requirements of the position of
  employment being sought. Certain limitations of range of motion may be
  acceptable for certain specific options or positions, in which case
  acceptance for employment will be noted specifically for that position
  or option only.

Other than the regulatory standpoint, reaching the top air traffic tower might be hard. There may not be elevators reaching all the way to the top. To save space, many use ladders, not even a staircase.
However, working as air traffic controllers does not always mean in the tower. Many radar rooms are ADA complaint and are wheel chair accessible.


text:
Why do airlines require passengers to return to their allocated seats for landing?
Airlines which allocate seats often make announcements prior to landing to request passengers return to their allocated seats. What is the motivation for this requirement, especially since I have never seen the requirement rigorously enforced by the crew (by requesting sight of the boarding pass).

The requirement is not simply a polite way of requesting standing passengers return to their seats – for two reasons:

Crews are typically explicit in their language when giving directions, such as requiring standing passengers be seated. It is clear from the phraseology and emphasis given in the announcements that returning to the allocated seat is a critical component of the request.
On a recent long-haul flight, a couple seated in my row were offered to relocate to vacant seats in an exit row for the duration of the flight, provided they returned to the allocated seats for landing. (They were not, at the time, standing.) Furthermore, in the event, only one member of the couple returned; the other remained in the non-allocated seats (an example of non-enforcement).

Some possible motivating factors I have considered:

Weight distribution – ensuring the flight envelope of the aircraft is not exceeded during critical phases of flight. However, I have encountered this situation on wide-body jets on long-haul flights (e.g. A346, A388), where a handful of passengers, of nominal mass, being situated elsewhere in the plane does not seem cause for concern.
Collection of personal effects – if passengers relocate after takeoff, they may leave personal belongings at their original seat, unwittingly or not.   A requirement to return to the original seat may:

trigger passengers to locate & take with them items left/forgotten at their original seat, reducing the cost of the airline returning these to passengers later.
improve the efficiency of disembarking by avoiding passengers who need to move against the flow to collect belongings elsewhere in the aircraft.
However, I have encountered this after long-haul flights with tens of hours of turnaround time on the ground, so eliminating a few minutes from the disembarking time of some passengers does not seem a high priority (and, in any event, the effect of reducing the overall exit time would be in the noise and difficult to quantify).

Limitation of privilege (hence, revenue protection) – passengers in a higher cabin tier may benefit from certain privileges upon landing, such as the possibility to disembark the aircraft more quickly. However, crew are normally hot on ensuring passengers do not self-upgrade to a higher cabin, so this would not seem to apply.
Emergency preparedness – for example, ensuring there is a sufficient cabin crew to passenger ratio in all areas of the aircraft to meet emergency / evacuation requirements. Such ratios may be upset in the event passengers relocate far from their original seat. (If so, why is this not an issue when in the cruise?)
Passenger identification – air crash investigators often use seating manifests to identify remains of deceased passengers, so this requirement could be to ease any future investigation in the event of an incident on landing. (Similarly, what about the rare likelihood of an emergency which rapidly develops while in the cruise, without opportunity for passengers to relocate?)

None of these reasons seem to entirely justify the requirement for this routine request or its existence across all manner of aircraft types.

My questions

What benefit do airlines or the wider industry gain from this requirement?
Why is it not rigorously enforced by crews?
How do airlines which do not allocate seats to passengers satisfy the same requirement when there is no published seating manifest in advance of passengers entering the aircraft, or why are they exempt from such requirements?

I've moved mid-flight on assigned seating airlines and have never been asked to return to my assigned seat. The only reason I can see this is if there is a problem, it is easier to identify where your body was sitting at the time of the crash versus where they found you.

It also stops the arguments that can be caused by people taking someone elses seat (to get closer to an exit etc.).

After a crash your body is spread over several square feet/meters and will not be identified reading the label on the chair... this is definitely not the main reason.

A few possible reasons:

In cases where there are a lot of people standing, you don’t want someone to go sit in the first available seat they find, only to have the original holder of that seat arrive a minute later (repeat as much as you like), causing confusion and delays. So in most cases it’s probably not that strictly enforced, it’s just a quick and easy way to avoid musical chairs at a time when crew are usually busy going around preparing the cabin for landing.
Some of the requirements (e.g. weight distribution) may be important on some aircraft and not on others in the same fleet. It’s much easier to have consistent language even if it does not apply in all cases. Note that even on larger planes, it may happen that weight could be shifted enough if the flight is not very full. I believe there was a thread on this topic not so long ago.
Sometimes a flight may depart with some equipment inoperative (I had the case once of a 747 with a faulty emergency slide for instance), you don’t want people in the affected area (which would only be a problem during takeoff and landing). There may also be faulty seats not immediately apparent, but which could become an issue during landing (faulty seat belt, missing life jacket, seat which doesn’t lock in the right position...). Those seats would have been blocked during check-in or boarding and nobody should have been assigned one of those seats.

All in all, I think it's more of a combination of factors and a "one size fits all" approach. Much easier to just tell everybody to get back to their assigned seats than to decide exactly if and when they really need to.
Of course, in cases where there are real specific security reasons (e.g. faulty seats), crew will usually double check they are not used and actually enforce the rule, but if they can save a few minutes at a busy time, that's always better.

Its a matter of legal requirement (under the FAA, and I presume the EASA has a similar reg). Strictly speaking its really more important that the passenger returns to a seat. Generally you are asked to return to your seat as it can be assured its empty and available for you. Under FAA regulations you are required to be wearing a seatbelt for landing and thus must be in a seat

14 CFR 121.311 - Seats, safety belts, and shoulder harnesses.
(b) Except as provided in this paragraph, each person on board an
  airplane operated under this part shall occupy an approved seat or
  berth with a separate safety belt properly secured about him or her
  during movement on the surface, takeoff, and landing. A safety belt
  provided for the occupant of a seat may not be used by more than one
  person who has reached his or her second birthday.

Weight and balance is important but not on a single passenger level i.e. on an airliner of decent size if a single passenger moved around it would be ok. If half the plane was empty and the passengers rearranged them selves there might be an issue.

How do airlines which do not allocate seats to passengers satisfy the
  same requirement when there is no published seating manifest in
  advance of passengers entering the aircraft, or why are they exempt
  from such requirements?

They are not exempt from the requirements but there are enough seats for everyone on the plane and as noted above its really important that you are belted in so taking an available seat will do in this case. On these flights generally speaking, you take a seat prior to takeoff and that somewhat becomes your seat for the flight. In my experience there is little if any mid-flight seat swapping.

Furthermore, in the event, only one member of the couple returned; the
  other remained in the non-allocated seats (an example of
  non-enforcement).

As noted above the policy is to be belted in, so the regulation was indeed enforced. The other member of the couple may have remained in the seat if they were the only person capable of preforming the exit row duties.

I figured it was to make identifying passengers easier in the event of a fatal crash.

@CrossRoads while this has been cited as being helpful in an investigation I have never seen anything indicating this is why people are asked to return to their assigned seats.

@Dave - minor reason I know, but in business class on larger aircraft, you want everyone in their allocated seats for landing so you can give their suit jackets back to them: identified by the boarding pass in the jacket usually.

Years ago I worked for an international airline, and we were told the purpose of sitting in an allocated seat was to help quickly identify bodies in the event of an accident. I can only imagine balance plays a part if you were in a small 8-9 seater. As for airlines like Ryanair, where you pay a supplement to avoid middle seats in a 3-3 configuration, I'm fairly sure it's to stop you reaping the benefit of an aisle or window when you didn't pay for it. On a recent Ryanair flight, a flight attendant said it was to do with aircraft balance, but considering there were just two passengers playing musical chairs at the time, I really doubt this was the true reason.

After a crash your body is spread over several square feet/meters and will not be identified reading the label on the chair... this is definitely not the main reason.

@sophit that very much depends on the nature of the crash, and it is often the case that bodies/seats are identified with precision— for example https://upload.wikimedia.org/wikipedia/commons/f/f8/Ua232injurymap.png

@randomhead: yes sure. But that picture simply states the cause of death depending on the position in the airplane. And actually the note in that picture just confirms that it is not always possible to connect the seat number with a passenger. If one of my beloved friend had a boarding pass 25E on that flight I would have wanted to see his face and not his boarding pass to be sure of his death...

I always heard, informally within the airline industry, that it was in case the aircraft crashed, meaning it was important everyone was in their 'departure-control' allocated seat so they could be identified in the case of an accident. Weight and balance is less important at this phase of the flight (compared to takeoff), and the rule doesn't seem to be religiously enforced regardless.

One other less morbid facet to getting people to stay in their assigned seats before departure is to make any seating discrepancies easier to sort out. Dupe seats, or mismatched counts between the departure control system and the boarding pass readers are a nightmare for the crew or ground staff to sort out if people have moved around. It's often caused by one or two people slipping through the aerobridge without the boarding pass scan (eg. for families with kids, groups etc.). It has to be resolved to close the flight (at least on systems like Amadeus), as it looks like a Fail to board (FTB).

And yet there are plenty of airlines that do just fine without having assigned seats at all.

"Do just fine" being a specious compliment when it comes to security. With no pax/seat reconciliation before departure, these airlines introduce a potential security risk that other airlines can pick up at that point.

As far as I'm aware, they're fully compliant with all security legislation. On the rare occasions where passenger counts don't match, they can clearly deal with that just as accurately as an airline with assigned seating: it will be slower, but that is a commercial consideration, not a security consideration. If it were a significant commercial consideration, they would have done something about it.

Dupe seating situations are not 'rare' at all (I have no idea where you got this idea from - despite improved systems, they're still the bane of ground staff). Unallocated seating makes the problem of dupe seats harder to deal with - right up at departure time when seconds count. I also know that some airlines have relatively quietly gone back to allocated seating (notice: I didn't say 'pre-allocated' seating) for security reasons. I'm aware of two, and I expect there are probably others.

"they can clearly deal with that just as accurately as an airline with assigned seating: it will be slower, but that is a commercial consideration" - not quite: it's both a commercial AND a safety issue together. Less efficient/slower processes introduce safety risks because humans are charged with implementing them. This is standard security process design thinking - "the paper is not the process" - it's people's behavior on top of the process that makes the outcome.


text:
What is the table top runway maximum slope?
What is the maximum permissible slope for a table top Runway (elevation 1600 m) to be made on hill top ?

Courchevel Airport I believe is the steepest public-use runway with an 18.6% grade. Operating in that airport requires a special endorsement and training.

What country? What type of aircraft and operators? If there's no regulatory limit, there's probably a practical limit but it would depend on those details.

I think that's left up the pilot's discretion.

I'm not completely sure what you're asking, but this question might be helpful

Most Part-25 certified aircraft have an operating limit of roughly +/-2% for runway slope, as most of the runways fall into this category.
It would be probably possible to certify aircraft for steeper slopes, however at a significant cost, as the flight test program would have to be extended to collect sufficient data.
It is also worth mentioning that anything over 1% upslope requires a bit of a different flare technique as opposed to a flat runway. Usually a bit earlier flare with a bit late thrust reduction does the trick. Extending the limit beyond 2% would probably require additional training, as the flare characteristics would be significantly different than that at a normal runway.

Well, it is certainly possible to certify aircraft for steeper slopes, and some of them are, because there are places like VNLK (Hillary Tenzing Airport, Lukla, 12% slope) and LFLJ (Courchevel Altiport, over 18% slope).


text:
Do the crew members in the plane have access to cargo area?
I always thought that if there is fire ir something else happening in the cockpit, can the crew members go in cargo area to secure the place..

Some cargo area's have fire suppression systems installed, but I don't know of any passenger aircraft that has access to the cargo area from the cockpit. Cargo aircraft are usually accessible.

@RonBeyer -- I believe that some commuter aircraft have no C compartments, only As and Bs...


text:
What did this ATC call mean?
Audio Clip
There is a rwy 24 in this airport. I'm not sure but the aircraft callsign likes 'TBN3BV'. I tried to find what the aircraft type is but I couldn't. Does somebody know what type of aircraft this is?
The aircraft was approaching to land and had number 3. I think there was traffic close to the aircraft. So the controller said make S-turn for safety...is it correct?
I sometimes make L/R360 or 270 to avoid other traffic but, I've never made S-turn while approaching to land.
I want to know what the controller said because I missed some word and I wonder if I can make S-turn while approaching to land. If I could, should I make two half circle?

Please only ask one question per post

They said "TBM" "Three-Bravo-Victor" (3BV). TBM is the aircraft make, a TBM and 3BV is the last 3 letters of the callsign.
The maneuver really isn't traffic avoidance so much as exactly what the controller said, spacing. They need to keep a minimum distance between traffic so having the TBM (a fast aircraft) perform an S-turn allows the aircraft in front of it more time to get further away.
Usually if you are in the pattern they will ask for a 360 turn, but if you are in a long straight-in and they just need a little bit of spacing, they will ask for the S-turn. For the S-turn approach you would simply turn 90 degrees to the course, then roll 180 degrees to face the opposite direction, then 180 degrees back around and 90 degrees back on course.

Thank you. That is TBM! When the aircraft got the landing clearance, it was 8 miles of the airport. That's why the controller have it make S-turn..

Probably this one: https://registry.faa.gov/aircraftinquiry/NNum_Results.aspx?NNumbertxt=43BV


text:
Has there been a recent change in the airspace configuration at KFYV-- Drake Field near Fayetteville AR?
Has there been a recent change in the airspace configuration at KFYV-- Drake Field near Fayetteville AR?  If so, where can we find an official description of that change?
KFYV -- Drake Field airport at Fayetteville Arkansas http://vfrmap.com/?type=vfrc&lat=36.005&lon=-94.170&zoom=10
(Memphis sectional chart, western portion of north half)
A sectional chart dated April 13 2006 shows a class D circle with a large E4 (dashed magenta) extension to the south, but on the current sectional chart (effective March 28 2019) the area projecting to the south is now much smaller and is class D rather than E4.
Has there been a recent change in the airspace here?
If so, what is the official FAA source that describes that change?
I do not see the airspace configuration as shown on the current sectional to be reflected in the August 2018 edition of the FAA's "Airspace Designations and Reporting Points" document ( https://www.faa.gov/documentLibrary/media/Order/JO_7400.11C.pdf ) , or in the more recent amendments given here https://www.faa.gov/air_traffic/publications/airspace_amendments/
The Class D airspace is described on page D-112 of the "Airspace Designations and Reporting Points" document, and the E4 airspace is described on page E-206.  The description matches what I see on the 2006 sectional chart.
Is the current sectional chart simply wrong?

You don't have to add "answered" to the title of the question, simply mark your answer as the answer and it will show up green in searches.

Got it.  Looks like it won't let me do that for two more days though.

No problem, just mark it when you can unless something better comes along. There is no issue here with answering your own questions, it is highly encouraged even.

A little more googling has provided an answer -- on 12/10/18, effective 2/28/19, the extension was greatly reduced in size (and the remaining bit converted to class D) due to the decommissioning of the Drake VHF omnidirectional range (VOR) navigation aid -- see https://www.federalregister.gov/documents/2018/12/10/2018-26498/amendment-of-class-d-and-e-airspace-and-revocation-of-class-e-airspace-fayetteville-ar
I'm not sure why that airspace change was not reflected in any of these documents-- https://www.faa.gov/air_traffic/publications/airspace_amendments/
Actually, it was there, I just didn't see it because they mistakenly used the abbreviation "AK" not "AR" for Arkansas in the table.
Nothing more need be said here--